FR2545289A1 - METHOD FOR PREPARING THE END OF A VERY HIGH FREQUENCY FLEXIBLE COAXIAL CABLE FOR THE POSITIONING OF A CONNECTOR ELEMENT AND SLEEVE USABLE FOR CARRYING OUT THE METHOD - Google Patents

Abstract

THE INVENTION RELATES TO A PROCESS FOR PREPARING THE END OF A VERY HIGH FREQUENCY FLEXIBLE COAXIAL CABLE FOR THE PLACEMENT OF A CONNECTOR ELEMENT, THIS CABLE PRESENTING A CENTRAL CONDUCTOR, A DIELECTRIC, AT LEAST ONE EXTERNAL CONDUCTOR. AND AN EXTERNAL SHEATH. AN END TRUNCON OF THE EXTERNAL SHEATH IS CUT AND REMOVED, WE PLACE ON THE OUTER SHEATH AND THE STRIPPED PART OF THE EXTERNAL CONDUCTOR (s) 3, 4 A SLEEVE 9 INCLUDING A RECESS INTERNAL IN THE FORM OF TWO CYLINDRICAL TRUNKS SEPARATED BY ONE TRUNK TRUNCONIC SO AS TO BRING THE END OF THE SHEATH 5 IN SUPPORT IN THEIT TRUNCONIC TRUNCON, THE STRIPED END OF THE EXTERNAL CONDUCTOR (s) 3, 4 PROJECTING BEYOND THE FRONTAL END OF THE SLEEVE, IN PARTICULAR FIXED BY SLEEVE ON THE EXTERIOR CONDUCTOR (S) IN THE AREA OF THE STRIPPED PART OF THE EXTERIOR CONDUCTOR SURROUNDED BY THE SLEEVE, AFTER WHICH IS CUT THE EXTERNAL CONDUCTOR (s) 3, 4 THEN DIELECTRIC 2 BEYOND THE FRONT EXTREMIT 15 OF THE SLEEVE 15 STRIP A TRUNK OF AN INTERIOR CONDUCTOR.

Description

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  The present invention relates to a method for preparing the end of a flexible coaxial cable at very high frequency for the implementation

place a connector element.

  Increasingly, for the transmission of very high frequency energy, flexible coaxial cables are being used instead of rigid coaxial lines which are not suitable for many applications, in particular

in aeronautics.

  Such flexible coaxial cables that can be used at very high frequencies usually comprise a multi-strand central conductor, in particular made of silver-plated copper, and at least one and preferably two outer conductors, the first preferably consisting of a wound ribbon, in particular of silver-plated copper, the second preferably a braid also made of silver-plated copper on the outside of the ribbon Between the central conductor and the first outer conductor is disposed a dielectric, in particular aerated or solid polytetrafluoroethylene (PTFE) Finally, around the second outer conductor is arranged an outer sheath, in particular extruded PTFE providing mechanical and chemical protection of the cable This sheath also keeps wound at the ends of the cable ribbon constituting the first

outside conductor.

  The applicant company has already described in its French patent 79 02468 a process for preparing the end of such a flexible coaxial cable to very

  high frequency for setting up a connector element.

  According to the method described in the previous patent, the end of the cable is first punched in several notches, in particular two or four notches, through the outer sheath so as to permanently deform the wound tape and then it is put in place. a sleeve, between the wound tape and a stripped portion of the braid so that the end of the sleeve is substantially right of the end of the sheath at the limit of the stripped portion of the braid, the sleeve being immobilized mechanically by crimping a ferrule on the sheath and the stripped portion of the braid and then welded on the wound tape Finally, the ribbon portion is unwound beyond the end of the sleeve and the ribbon is cut and the dielectric flush with said end

  sleeve leaving bare a section of inner conductor.

  A coaxial connector made by placing a connector element on each end of coaxial cable thus prepared, while being very interesting in practice, nevertheless has an imperfection in this respect.

  concerning the transmission characteristics.

  This disadvantage results from the fact that there is in a connector element thus mounted at the end of a flexible coaxial cable at very high frequency a transition of a certain length between the end of the sheath.

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  the cable, which corresponds to the end of the homogeneous structure of the cable, and the beginning of the coaxial line of the connector This transition which constitutes a zone of disturbances provides additional reflection of the transmitted signal and therefore an increase in the reflection coefficient due to the connector On the other hand, when, as is usually the case, the first outer conductor is a wound tape, the latter loses some of its electrical continuity characteristic between the end of the cable jacket and the rear end of the sleeve. This disturbance causes small variations in contact resistance at high frequency between the coiled ribbon turns in the disturbance zone thus produced, which results in instabilities of power losses in the coaxial cord when

  causes flexing of the cable very close to its output from the connector.

  The present invention proposes to provide a method for preparing the end of a very high frequency flexible coaxial cable avoiding the presence of disturbance zones between the end of the complete coaxial cable.

  and the beginning of the coaxial line of the connector.

  The process according to the invention is essentially characterized by the fact that an end section of the outer sheath is cut and removed, the sleeve or the external conductor is placed on the outer sheath and the outer part, a sleeve comprising a inner recess formed of two cylindrical sections separated by a frustoconical section, so as to bring the end of the sheath bearing in said frustoconical section, the stripped end of the outer conductor or conductors protruding beyond the front end of the sleeve the sleeve is fixed, in particular by welding, to the outer conductor or conductors in the zone of the stripped part of the outer conductor or conductors surrounded by the said sleeve, after which the outer conductor or conductors are cut and the dielectric flush with the end

  front of the sleeve-leaving bare a section of inner conductor.

  In the case where the one or one of the outer conductors is a ribbon, the end of the cable is preferably punched in several notches, in particular two or four notches, through the outer sheath so as to deform

  permanently the external conductor (s).

  Once the end of the cable has been thus prepared, the procedure is as described in the aforementioned prior patent and, for this purpose, is provided on the stripped central conductor of the cable end an insulator bearing against the front end of the sleeve, the central contact of the connector is mounted on the central conductor resting on the insulator, the central contact is welded to the central conductor, the end of the cable is mounted in the connector body and the assembly is immobilized by screwing a plug

back.

  The subject of the present invention is also a sleeve that can be used for carrying out the method which, as mentioned above, comprises an internal recess comprising a cylindrical rear insertion section of appropriate diameter and length to ensure a good guiding of the end of the cable introduced and absorb the flexions to which the cable may be subjected very close to the sleeve. Preferably, the diameter of this rear cylindrical section of the recess is slightly greater, especially from 0.1 to 0, 2 mm to the outer diameter of the sheathed cable, the length of this section being preferably at least 0.6 times the outer diameter of the cable. As an extension of this cylindrical introduction section, the recess of the sleeve comprises a frustoconical central section, narrowing towards the front of the sleeve and whose cone angle is appropriate to allow the penetration of the outer conductor (s) of the ble through the sleeve and the tightening of the end of the cable sheath on the frustoconical bearing surface of the recess regardless of the variations in the outer diameter of the cable In practice, and according to the nature of the cable, this angle can be advantageously

  between about 10 and 45 and preferably of the order of 150.

  Beyond this frustoconical central section the recess is extended by a cylindrical front section of diameter smaller than the diameter of the rear section, suitable for the passage of the outer conductor or conductors of the cable without changing their structure the length of the cylindrical section before the recess of the sleeve is determined to allow efficient attachment of the sleeve, in particular by welding, on the outer conductor or conductors of the cable, the length of this section being preferably in practice substantially

equal to its diameter.

  At its front end, the sleeve advantageously comprises a flange in the form of a collar intended to allow it to be fastened in the connector, the end face of the flange ensuring the electrical connection between the end of the outer conductor or conductors of the cable and the beginning of the line.

coaxial connector.

  It is understood that, although the homogeneous structure of the cable physically stops at the end of the cable sheath located in the frustoconical central section of the sleeve recess, the sleeve will in fact extend this homogeneous structure of the cable up to 'at the end of the driver (s)

  outside the cable avoiding disturbance areas.

  The method according to the invention can be implemented to produce straight connectors or angled connectors, in which case, it is sufficient

  use a sleeve of appropriate bent shape.

  In order to better understand the invention will now be described by way of example in no way limiting an embodiment with reference to the accompanying drawing in which: Figure 1 shows in partial section a coaxial cable flexible at very high frequency usable for the implementation of the invention, Figure 2 illustrates the mounting of a connector element at the end of a cable prepared by implementing the known method according to the French patent 79 02468, FIG. 3 is an enlarged sectional view of a sleeve that can be used in the context of the present invention; FIGS. 4 to 8 schematically illustrate the implementation of the method according to the invention to prepare the end of a flexible coaxial cable according to Figure 1, Figure 9 is a view similar to Figure 2 of a connector element mounted at the end of a cable prepared by the implementation of the method according to the invention, Figure 10 is a e view similar to Figure 9 illustrating the mounting of a connector element by implementing the method according to

  the invention using a bent sleeve.

  FIG. 1 illustrates the structure of a very high frequency coaxial cable of a type commonly used and already described elsewhere in the art.

  French Patent No. 79 02468 This cable comprises a conductor -

  central 1 silver copper, multi-strand, a diéléctrique 2, including PTFE airfoil or full, a first outer conductor 3 in the form of a ribbon wound silver copper, a second outer conductor in the form of a braided silver-plated copper 4 and an outer protective sheath,

for example extruded PTFE 5.

  Figure 2 illustrates the mounting in a connector element of a

  such coaxial cable prepared as described in French Patent 79 02468.

  As described in this prior document during the preparation of the end of the cable, a sleeve 6 having an end flange 7 has been put in place, the tubular part of the sleeve being placed between the two outer conductor layers one of which in the form of ribbon 3, the other in the form of a braid 4 The sleeve was mechanically immobilized by crimping a ferrule on the sheath and the stripped portion of the braid, and then welded onto the

wrapped ribbon.

  As shown schematically in FIG. 2, there exists in such an assembly two disturbance zones designated respectively by A and B. Zone A corresponds to the transition between the end of sheath 5 of the cable, which corresponds to the end of the homogeneous structure of the cable, and the beginning of the line of the connector beyond the front face of the flange 7 of the sleeve, the zone B corresponding to the transition at the outer conductor in the form of a braid 4 between the end of sheath 5 and

  the rear end of the sleeve 6.

  FIG. 3 illustrates, in enlarged view, a usable sleeve

  for carrying out the method according to the present invention.

  This sleeve generally designated 9 has a recess

  interior 10 consists of three successive sections 11, 12 and 13.

  The rear portion 11 of cylindrical shape has, in the example illustrated for a cable with a maximum diameter of 5.2 mm, a diameter of 5.3 mm and a length of 6 mm This cylindrical section 11 is extended by a section frustoconical 12 which, in the illustrated example, has a length of 2.3 mm and an angle at the apex of 150 This section 12 is itself extended by a cylindrical front section 13 which, in the illustrated example, has a

  length of 5 mm and a diameter of 4.7 mm.

  At its front end the sleeve 9 has a flange-shaped flange 14 defining a front face 15 which will ensure the electrical connection between the end of the outer conductors of the cable and the beginning

of the coaxial line of the connector.

  Referring now to Figures 4 to 8 to describe the method according to the invention for the preparation of the end of a coaxial cable at very high frequency of the type shown in Figure 1 using a sleeve such as

described in Figure 3.

  With the aid of a jaw punch pliers, preferably having two opposing internal bulges in section, the end of the cable is punched in two or preferably four notches 16 through the outer sheath 5 of the cable. This has the effect of to permanently deform the wound tape 3 preventing it subsequently to unfold It is seen in Figure 3 the end of the cable after punching This phase of punching obviously has reason to be that in the case o the cable includes a

  outer conductor-in the form of coiled ribbon.

  As illustrated in FIG. 6, the sheath 5 of the cable is removed over a certain length at the end of the cable, revealing a braid section 4. This stripping length must in practice be at least equal to the distance which must be separate the end of the sheath from

  the end of the central conductor in the fully assembled state of the connector.

  As seen in FIG. 7, the cable thus prepared is inserted into a sleeve 9 until the front end of the sheath 5 comes into position.

  bearing against the frustoconical bearing surface of the section 12 of the recess of the sleeve 9.

  This frustoconical extent of the recess of the sleeve facilitates the insertion of the outer conductors of the cable and prevents strands of the

  braid 4 are pushed back into the sleeve.

  The subsequent phase of preparation consists in welding the outer conductors 3 and 4 of the cable and the sleeve by a low-temperature solder, for example tin-lead at 180 ° C. The welding should preferably be carried out over the entire portion of the outside conductors lying within the

  sleeve, zone shown schematically by the double arrow of length S in FIG.

  This zone extends in fact between the front end of the sheath 5 and the face

  front end 15 of the sleeve.

  As can be seen in FIG. 8, the outer conductors 3 and 4 and the dielectric 2 are then cut to the right of the end face 15 of the sleeve. If necessary, the end of the inner conductor 1 is cut off at a distance from the end face 15 adapted to the mounting of the

central contact of the connector.

  FIG. 9 shows the mounting of a connector element on a cable end thus prepared. In order to carry out this assembly, as already described in French patent 79 024689, an insulator 17 is provided on the stripped central conductor 1. the end of the cable bears against the front face 15 of the sleeve 9 is then mounted the central contact 18 on the central conductor 1 bears on the insulator 17 and soda

  the central contact 18 on the central conductor 1, as indicated in 19.

  The coaxial cable, welded by its central conductor to the central contact, is then placed in a connector body 20 and immobilized.

  the assembly by screwing a rear cap 21.

  For producing a bent connector element as illustrated in FIG. 10, the same process steps are implemented using the same components except for a sleeve 9 'which has a bent shape and a recess whose front section has a significantly longer length

  large than in the right connector embodiment according to FIG. 9.

  Although in the example illustrated a coaxial cable with two outer conductors, one consisting of a wound tape and the other constituted by a braid, has been used, the method according to the invention is not limited thereto and may be implemented with any other type of flexible cable, in particular of the type comprising a single outer conductor, in the form of a braid, ribbon wound or constituted by helicoidal strands not braided, or for example of the type with two outer conductors each consisting of a braid. 7 - Finally, it is obvious that the invention is not limited to the particular embodiment of implementation described and can be made various modifications without departing from its scope or its spirit.

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Claims (5)

  1 Process for preparing the end of a very high frequency coaxial flexible cable for setting up a connector element, said cable having a central conductor, a dielectric, at least one outer conductor and an outer sheath, characterized in that an end section of the outer sheath is cut and removed, a sleeve (9, 9 ') comprising the sleeve (9, 9') comprising the outer sheath and the stripped portion of the outer conductor (s) (3,4) is placed. an inner recess (10) formed of two cylindrical sections (11; 13) separated by a frustoconical section (12) so as to bring the end of the sheath (5) abutting into said frustoconical section, the stripped end of the outer conductor or conductors (3,4) protruding beyond the front end of the sleeve, the sleeve is fastened, in particular by welding, to the outer conductor or conductors in the zone (S) of the stripped portion of the external conductors surrounded by said sleeve, after which the outer conductor or conductors (3,4) are cut and the dielectric (2) beyond the end (15) of the sleeve leaving a portion of inner conductor (1).   2 Method for setting up a connector element on the end of a high-frequency coaxial cable, characterized in that after having prepared the end of the cable by the method according to claim 1, it is arranged on the conductor central stripped of the end of the cable an insulator (17) bearing against the end end face (15) of the sleeve, the central contact (18) of the connector is mounted on the central conductor (1) resting on the insulation (17), the central contact is welded to the central conductor, the end of the cable is mounted in the connector body   (20) and the assembly is immobilized by screwing a rear plug (21).   3 sleeve usable for the implementation of the method according to one   any of claims 1 and 2, characterized in that it comprises   an inner recess (10) having a cylindrical rear insertion section (11), a central frustoconical section (12) narrowing towards   the front of the sleeve and a front cylindrical section (13).   4 sleeve according to claim 3, characterized in that the frustoconical portion (12) has an angle of c 6 ne (î) between approximately     and about 450 and preferably of the order of 150.   Sleeve according to any one of claims 3 and 4,   characterized in that it comprises at its end end a flange-shaped collar (14) whose front face (15) provides the electrical connection between the end of the outer conductors or conductors of the cable and the   beginning of the coaxial line of the connector.